Residential spas are widespread sources of enjoyment and relaxation. Such spas are typically formed with dimensions several feet on a side. Spas may be located in the ground, within a gazebo, or surrounded by a deck. They are preferably covered when not in use both to maintain water temperature and to prevent contamination of the spa water. Spa covers typically employ a rigid frame across which a cover of wood, fabric, or plastic is spread.
Due to its considerable mass, a spa cover mounted on a conventional mounting system is quite heavy to lift from a closed position into an open position. Considerable strength is required to lift the spa cover through an arc of ninety degrees in moving it to cover and uncover the spa tub. At present there are various assist mechanisms available for moving a spa cover between open and closed positions. Conventional spa covers, when moved from a position covering the spa into an open position, are sometimes mounted on hinge mechanisms which allow the spa covers to be rotated between a generally horizontal orientation above the surface of the spa and a generally vertical orientation extending upwardly along one edge of the spa deck.
U.S. Pat. No. 5,566,403 describes a spa cover lift apparatus, which uses gas springs to aid in the lifting process. The described apparatus is susceptible to damage to the gas springs due to overstretching the spring with the cover in the upright position. With the cover in the upright position, forces due to wind gusts or improper use can tend to rotate the cover past the upright position, placing a stretching force on the gas spring. This can cause failure of the gas spring. Another disadvantage of the lift apparatus described in this patent is that, due to the pivotal connection of the spring to the lifting arm and spa, the spring will exert considerable lifting force when the cover is in the closed position. This can assist the cover being opened under undesired circumstances, e.g. due to wind gusts.
It would therefore represent an advantage to provide a spa cover lift system which provides protection against overstretching the assisting spring at the upper travel limit.
It would further be an advantage to provide a spa cover lift system which provides little or no lift assistance when the spa cover is in the covered position, and which rapidly provides increased lift assistance after the cover has been lifted away from the top of the spa.